From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030320AbWARJVa (ORCPT ); Wed, 18 Jan 2006 04:21:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030321AbWARJVa (ORCPT ); Wed, 18 Jan 2006 04:21:30 -0500 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:16017 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S1030320AbWARJV3 (ORCPT ); Wed, 18 Jan 2006 04:21:29 -0500 Subject: Re: io performance... From: Alan Cox To: "Jeff V. Merkey" Cc: Max Waterman , linux-kernel@vger.kernel.org In-Reply-To: <43CDC44E.6080808@wolfmountaingroup.com> References: <43CB4CC3.4030904@fastmail.co.uk> <43CDAFE3.8050203@fastmail.co.uk> <43CDC44E.6080808@wolfmountaingroup.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Wed, 18 Jan 2006 09:21:04 +0000 Message-Id: <1137576064.25819.11.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Maw, 2006-01-17 at 21:30 -0700, Jeff V. Merkey wrote: > > How can I force it to be 'write back'? > Forcing write back is a very bad idea unless you have a battery backed > up RAID controller. Not always. If you have a cache flush command and the OS knows about using it, or if you don't care if the data gets lost over a power failure (eg /tmp and swap) it makes sense to force it. The raid controller drivers that fake scsi don't always fake enough of scsi to report that they support cache flushes and the like. That doesn't mean the controller itself is neccessarily doing one thing or the other.